1. Field of the Invention
The present invention relates generally to magnetic heads in disk drives, and more particularly to magnetic write heads configured to write data at high data rates.
2. Description of the Related Art
Prior art magnetic write heads have serious impediments for writing data at today""s ever-increasing high data rates. Such write heads either cannot produce enough magnetic flux within the short cycle times available during high frequency operation to write sufficiently to a storage medium or, if structurally compensated to produce enough flux to write sufficiently during high frequency operation, they tend to produce excessive flux during low frequency operation such as to cause undesirable side-writing or adjacent track interference (ATI).
To illustrate, FIG. 1 is a planar view of a conventional magnetic write head 100 for writing to a storage medium, such as a disk 102, wherein the driving coil is omitted from the diagram for clarity. Write head 100 is made from pole pieces which form a write gap 104 at an air bearing surface (ABS), where magnetic flux is produced for writing data to disk 102. Write head 100 has a flare point 106 and a flare angle 108 with dimensions that may not be sufficient for writing at high data rates. That is, the magnetic flux that can be produced at write gap 104 within the short cycle times available during high data rate operation is not sufficient to write data to disk 102, especially at today""s high level of disk coercivity (e.g., 4000 Oersteds or greater).
In FIG. 2, a magnetic write head 200 which is configured to sufficiently write data to disk 102 at high data rates is shown. The high data rate may be, for example, one that is greater than or equal to 500 MHz. Similar to write head 100 of FIG. 1, write head 200 has a flare point 206 and a flare angle 208. However, so that write head 200 can sufficiently write at a high data rate, flare point 206 of write head 200 is shorter in length than flare point 106 of write head 100 (i.e., the flare point is closer to the ABS), and/or flare angle 208 of write head 200 is greater than flare angle 108 of write head 100. For example, flare point 106 of write head 100 is 1.0-1.5 xcexcm whereas flare point 206 of write head 200 is 0.5-1.0 xcexcm, and flare angle 108 of write head 100 is 30xc2x0 whereas flare angle 208 of write head 200 is 60xc2x0.
Although write head 200 is capable of producing adequate flux to write at high data rates, it may produce excessive flux when writing at low data rates which tends to cause undesirable side-writing and interference on disk 102. This is because the magnetic materials making up the pole pieces (i.e., the wide magnetic core or xe2x80x9cyokexe2x80x9d in the back, and the relatively narrow pole tips in the front) have a magnetic permeability that is frequency-dependent and decreases as the operating frequency increases. Put another way, the efficiency of a conventional write head is much better at low frequencies than it is at high frequencies. This phenomenon will be referred to herein as xe2x80x9cefficiency roll-offxe2x80x9d of the write head.
To further illustrate this low frequency situation, FIG. 3 shows a pole tip view of write head 200 of FIG. 2 which reveals a pole piece 302 (e.g., P2) and a pole piece 304 (e.g., P1) forming write gap 204. In this example, write head 200 is writing data at a low data rate where magnetic fluxes 306 are undesirably produced excessively in areas away from write gap 204. This is likely to cause interference to other data written on adjacent tracks on disk 102. Unfortunately, write head 200 may therefore not be usable since it will overwrite and erase where it should not be doing so, resulting in a large erase-band and high level of ATI. This problem is only exacerbated by today""s required high recording density and, in particular, a large number of tracks-per-inch. For example, today""s high recording density is greater than 50 kilotracks per inch (KTPI).
Referring to FIGS. 4A-4C, timing diagrams related to the production of magnetic flux at write gap 204 of write head 200 of FIG. 2 are shown. These diagrams help to illustrate the interference issues that must be considered when using the geometry of high-frequency write head 200. More particularly, FIG. 4A is a timing diagram for high frequency operation; FIG. 4B is a timing diagram for low frequency operation; and FIG. 4C is a timing diagram for DC operation (lowest frequency=0 MHz which is typical for data erasure). The binary write current sequencing scheme used throughout FIG. 4 is represented in the well-known Non-Return-to-Zero (NRZ) format, where xe2x80x9c1xe2x80x9d represents one current or magnetization direction and xe2x80x9c0xe2x80x9d represents the opposite direction.
In FIG. 4A, a data signal 402 represents high speed data in binary form (xe2x80x981xe2x80x99 for binary one and xe2x80x980xe2x80x99 for binary zero) to be written to disk 102, and a flux signal 404 represents magnetic flux which appears at write gap 204 of write head 200 to write the high speed data to disk 102. As illustrated, data signal 402 reflects the binary write current sequence xe2x80x9c10101010xe2x80x9d to be written to disk 102. Data signal 402 has a frequency for writing data to disk 102 at a high data rate, which may be any suitable data rate that is higher than the nominal rate or average rate of writing using write head 200. This high data rate may be the maximum operating frequency of write head 200, which exists when bit transitions (xe2x80x9c1xe2x80x9d to xe2x80x9c0xe2x80x9d or xe2x80x9c0xe2x80x9d to xe2x80x9c1xe2x80x9d) occur for each one of a plurality consecutive cycles. The high data rate may be, for example, 500 MHz or greater, or even 1 GHz or greater. As a result of writing at the high data rate, flux signal 404 peaks at a high data rate flux level, which is desirably lower than a maximum flux level beyond which excessive side-writing and interference with other data tracks on disk 102 would tend to occur.
In FIG. 4B, a data signal 406 represents low speed data in binary form to be written to disk 102, and a flux signal 408 represents the magnetic flux which appears at write gap 204 of write head 200 to write this low speed data to disk 102. As illustrated, data signal 406 reflects the binary write current sequence xe2x80x9c11001100xe2x80x9d to be written to disk 102. In contrast to data signal 402 of FIG. 4A, data signal 406 of FIG. 4B has a frequency for writing to disk 102 at a low data rate, which may be any suitable data rate that is less than or equal to the nominal rate or average rate of writing using write head 200. This particular example reflects a data rate that is half of the high data rate described in relation to FIG. 4A. Referring to the previous example of FIG. 4A, the low data rate may be 250 MHz or less. As a result of writing at this low data rate, flux signal 408 may peak at or exceed the maximum flux level, beyond which excessive side-writing and interference with other data on disk 102 tends to occur. In FIG. 4C, a data signal 410 illustrates DC operation (binary data sequence of xe2x80x9c11111111xe2x80x9d) which also causes flux signal 412 to peak or exceed the maximum flux level at which interference tends to occur.
For a write head that has been structurally compensated for high data rates, excessive flux generation during low data rate operation is very likely to happen. This is due to the efficiency roll-off phenomenon previously referred to: a write head configured to have good efficiency at a high data rate will have an even higherxe2x80x94perhaps even excessively higherxe2x80x94efficiency at a low data rate.
Thus, as shown and described in relation to FIGS. 2-4, a write head that is geometrically configured so that sufficient flux is produced during high data rate operation tends to cause excessive side-writing or ATI during low data rate or DC operation. Accordingly, what is needed is a magnetic head that has the ability to write data at high data rates but also produces minimal interference when writing data at low data rates.
A magnetic head configured for high data rate operation has first and second pole pieces (which include the wide magnetic core or xe2x80x9cyokexe2x80x9d in the back, and the relatively narrow pole tips in the front), a write gap formed between the first and second pole pieces, and at least one magnetic shunting element extending between the first and second pole pieces which is magnetically in parallel with the write gap. The at least one magnetic shunting element serves as a low frequency attenuator in the magnetic head.
The magnetic head is configured to write data at a high data rate where a sufficient magnetic flux is produced at the write gap, and configured to write data at a low data rate where the at least one magnetic shunting element shunts magnetic flux excess so that a reduced magnetic flux is produced at the write gap. This reduced low frequency or DC magnetic flux does not exceed the maximum flux beyond which excessive side-writing and adjacent track interference (ATI) would otherwise begin to occur.
Thus, excessive magnetic flux is advantageously shunted by the at least one magnetic shunting element to reduce interference that would otherwise occur when writing at the low data rate, but not when writing at the high data rate where additional magnetic flux is needed for sufficient writing.